Conventionally, it is required that various types of information related to radiation amounts be displayed for the purpose of managing radiation exposure. For example, it is known that an Exposure Index (EI) and a Deviation Index (DI) are required to be displayed, which are defined as IEC 62494-1 by the International Electrotechnical Commission (IEC). In this situation, the exposure index is a value indicating an amount corresponding to an incident-to-detector radiation amount (D) calculated from a representative pixel value (V) of an image. The exposure index is a uniform index for radiation amounts that can be used even if systems from different manufacturers are being used. Further, the deviation index is an index value indicating how much difference is exhibited by an “EI” obtained for each image taking process, with respect to a “Target Exposure Index (EIT)”. The deviation index can be calculated by using an expression “DI=10 log10(EI/EIT)”. In this situation, “EIT” is an intended “EI” value that is set for each medical examination.
While it is required that various types of information related to radiation amounts (hereinafter, “exposure”) be displayed as noted above, examples of known techniques used for displaying an exposure index, a deviation index, and a target exposure index include a technique by which, for example, an exposure index and a deviation index are calculated every time an image taking process is performed, so that the exposure index and the deviation index that were calculated as well as a target exposure index are displayed as a result of the image taking process.